Doesn't the undo functionality cause it to store copyrighted data from the original ROM in the patch?
I think it's similar to adding a note to a book, and then removing that note, leaving you with a the original book. That scenario doesn't violate copyright law as far as I'm aware.
That's not how patching a rom works. You directly replace data and the formats that let you undo have to put a copy of the original data in the patch file. So yes it is a risk.
You don't need a copy of the original data, you can simply store your change as a XOR so undoing it mean XORing it again.
However, if your change involves zeroing something out, you're back to storing the original data again.
> nyuu.page
Is this in any way related to byuu, the SNES emulator author?
No it's not related, sadly Byuu passed away several years ago.
> It is written in Haskell and Rust and this made getting it to work nicely in the browser, interesting
I imagine. What motivated using that combination?
I recently stumbled upon https://www.hackdex.app/ which is a lovely website dedicated to Pokémon ROM hacks.
It's a really vibrant scene, with a lot of different hacks that go all the way to fully-fledged games, but because it's so rich it can be a pain to find what is available and what the latest version of a given ROM hack is.
This website has a neat feature where you upload any base Pokémon ROM file, and it filters all available ROM hacks that are compatible with it via a neat UI. And of course it offers you a one-click download (well, in-local-storage-patch) to the given ROM hack.
Source code: https://github.com/Hackdex-App/hackdex-website
Quick clarification: I'm pretty sure there's no uploading at all; it uses local storage for the filtering too, which is important because uploading a ROM tends to be risky legally